Load GitLabSchema as workaround for errors

What does this MR do?

This MR loads GitLabSchema as a workaround for errors we see due to a lack of thread safety (see #211478 (comment 320636547)).

We can remove this workaround when we convert the schema to use the new query interpreter runtime #210556 (closed).

• Issue: #211478 (closed)

Does this MR meet the acceptance criteria?

Conformity

• [-] Changelog entry
• [-] Documentation (if required)
• Code review guidelines
• Merge request performance guidelines
• Style guides
• [-] Database guides
• [-] Separation of EE specific content

Availability and Testing

• [-] Review and add/update tests for this feature/bug. Consider all test levels. See the Test Planning Process.
• [-] Tested in all supported browsers
• [-] Informed Infrastructure department of a default or new setting change, if applicable per definition of done